In high speed digital circuits, fast doesn’t necessarily mean “high clock rate”. [Jack Ganssle] does an excellent job at explaining how the transition time of signals in high speed digital circuits is just as important as the speed of the signal itself. When the transition time is large, around 20 nanoseconds, everything is fine. But when you cut it down to just a few nanoseconds, things change. Often you will get a ringing effect caused by impedance mismatch.
As the signal travels down the trace from the driver and hits the receiver, some of the signal will get reflected back toward the driver if the impedance, which is just resistance with a frequency component, does not exactly match. The reflected signal then heads back to the driver where the impedance mismatch will cause another reflection. It goes back and forth, creating the ‘ringing’ you see on the scope.
[Jack Ganssle] goes on to explain how a simple resistor network can help to match the impedance and how these should be used in circuits with fast transition times, especially where you will be taking readings with a scope. As the scope probe itself can introduce impedance and cause the ringing.
In case you didn’t pick up on it, [Jack Ganssle] also happens to be one of the judges for The Hackaday Prize.
Continue reading “Delving Deep into High Speed Digital Design”
A (long) while ago I presented you the Easy-phi project, which aims at building a simple, cheap but intelligent rack-based open hardware/software platform for hobbyists. With this project, you simply have a rack to which you add cards (like the one shown above) that perform the functions you want.
During these last months my team has been finishing the design and production of several different boards so I’ll start showing them off during these next weeks. Today I present you the High Speed Logic Gate Board, a quantum-physicist requested easy-phi module that can perform logic AND/OR functions at <2GHz speeds. This quite technical write-up is mainly about the constraints that high-speed signals pose for schematics design but is also about the techniques that are used for HS signals termination and monitoring. I hope, however, it’ll give our readers a nice overview of what the insides of a high-speed system may look like. All the files used for this board may be found on the official GitHub repository.
[Limpkin] designs circuits for a living. This board is one of his recent projects, and although his skills are light years ahead of our own experiences, he did a pretty good job of explaining how he put this board together.
He was tasked with measuring the light intensity of two photodiodes. The expected impulses picked up by those components will be less than a nanosecond in duration, putting some special design constraints upon him. To register this signal he’s using three cascading op-amps per input. To ward off false readings from RF interference he also designed in the shielding which you see surrounding the majority of the circuit.
His package choice for the THS3202 op-amps is quite interesting. He didn’t go with the footprint that includes a thermal pad to dissipate heat because he didn’t want to interrupt the ground plane on the underside of the board. To keep the parts from melting he added an aluminum spacer that contacts the top of the package, then a heat sink that covers the entire shield frame. In a future revision he figures he’ll move to a four-layer board so that the can opt for the MSOP package that does the work for him.
This robot juggler, pictured above during its appearance at Amper 2010, can keep five balls in the air at once. It was designed by the Department of Control Engineering at the Czech Technical Institute in Prague. We know it doesn’t look like much in that still image, but the two videos embedded after the break are pure gold.
To arms on vertical tracks do the juggling. They can move up and down on said tracks, and circular grippers attached to each can pivot horizontally. A third actuator resides at the bottom of the machine, collecting any balls that might drop, and launching them back into the realm of the juggling hands. A high-speed camera facilitates object tracking in much the same ways that it’s been used for quadcopter control.
The objects being thrown around in that protective enclosure are billiards balls. We guess the added mass helps to dampen any small irregularities in the throw or the catch.
Continue reading “Robot juggler sure handles a lot of balls”
This method of book digitization allows you to scan an entire book by fanning through the pages. It uses a high-speed camera that captures 500 frames per second to get a good look at each page. Processing software isolates each pages, analyzes any curve in the paper due to the flipping, and smooths out the image for better optical character recognition results. The greatly reduces the time it takes to digitize a book, even compared to setups that automatically flip pages.
[Maurice] let us know that his latest photography tool for hackers, the Camera Axe 3.0, is now available. The original allowed you to trigger a high-speed flash and camera from a multitude of sensors, including light and sound. The new one does all that, but also: allows multiple cameras or multiple flashes, clean up of software to make it more user adaptable, and the best (arguably the most important) part – cheaper components! All that and more under the Creative Commons that we do love so much. Keep up the amazingly detailed and just pure awesome work [Maurice].
Popped balloons or bullets fired into apples, anyone can photograph with a quick sound based camera rig. Lasers have been used forever in motion detection. And even door bell chimes have been used before for remote camera shutter releases. No, [SaskView] wanted to go further and created his Laser Triggered High-Speed Photography setup, to photograph (of all things) milk splashes. We liked the simplicity of the project however; requiring no programmed microchips or overly complicated circuitry – rather he took a quick trip to the local dollar shop, used the amazing CHDK firmware, and he produced perfect results every time.
[Update: CHDK, not CHKD firmware. My mind must be elsewhere. Thanks jbot and agent smith]